Lake sedimentological and ecological response to hyperthermals: Boltysh impact crater, Ukraine

Past hyperthermals and associated negative carbon isotope excursions (CIEs) are inferred to have had significant impact on marine environments; however, still little is known from terrestrial ecosystems due to the lack of complete and high-resolution data. Here, we present a detailed sedimentological study from a borehole drilled in the K/Pg Boltysh impact crater (Ukraine) which was filled with a c. 400 m thick succession of Early Danian lacustrine sediments. A part of this succession was deposited during the Early Danian Dan-C2 hyperthermal as inferred from a negative shift in the carbon isotopes.

We use a combination of sedimentological, palynological and geochemical data to characterise lake sedimentological and ecological development across the CIE and 2) to assess the environmental effect of hyperthermals on terrestrial ecosystems. Based on detailed facies analysis, 5 distinctive gradual stages of lake evolution are identified, indicating a strong relationship to carbon isotope shifts and associated climatic trends. Initial pre-CIE sedimentation was controlled by crater morphology and crater rim erosion. During the main phase of the CIE, sediment supply was increasingly characterised by inflow-evaporation ratio variabilities which affected seasonal stratification patterns and longer-term lake levels. An inferred increase in atmospheric p_CO2 during the CIE, together with increasing mean annual temperatures, was likely responsible for periodic increases in bioproductivity.

Orbital paced moisture availability oscillations derived from palynological data largely correspond to fluctuations in lake facies and lake levels, and suggest that long term lake evolution patterns are astronomically controlled. The gradual decline in sediment supply prior to CIE inception suggest that the Dan-C2 event did not initiate sedimentary changes, but amplified and promoted sedimentary response to orbital controlled climate change.